1. Field of the Invention
The present invention relates generally to the field of computer graphics.
2. Related Art
Computer graphics systems typically store digital format display images in a frame buffer, wherein the rows and columns of the frame buffer correspond to the rows and columns of the display monitor. A graphics rendering engine generates and stores the pixels for the display images in the frame buffer. A graphics processor then extracts the pixels for the display images, formats them, and sends them as a video frame. A digital to analog converter between the graphics processor and the display monitor converts the video frame into an analog video signal for the display monitor.
Alternatively, display images may be transferred from the frame buffer to a graphics post-processor which performs additional graphics processing on the display image prior to digital to analog conversion and display. For example, some computer graphics systems interpose post-processing between an image generation system and a display to perform window processing. The display images are supplemented with window ID information provided by the image generation system. Window ID information is generally considered auxiliary pixel data that identifies pixels as part of an area of the display (i.e., a window). Each window ID value is associated with a set of characteristics and features common to pixels within that window. For example, one window may contain monochrome pixels while another contains color pixels. The window ID information is used to modify the display images, which are then transferred to the display. Other computer graphics systems provide post-processing to perform various image enhancements, for example color translation.
In computer graphics systems in general, it is sometimes desired to transfer display images from a frame buffer to a post-processor supplemented with additional auxiliary information, e.g., window ID or illumination intensity. Communicating this auxiliary data from the image generation system to the post-processor has typically required implementing custom interfaces, for example, by providing a separate auxiliary data interface or by adding special operational modes to a video interface. Such custom interfaces, however, add cost and significant complexity.
Although various techniques are known for supplementing analog video data with additional information encoded during the blanking intervals, a digital data format and transfer mechanism is desired since both the frame buffer and post-processor handle data in a digital format. In addition, digital displays with digital interfaces are now being used.
Known digital video interfaces, such as the Digital Visual Interface (DVI), are available which can transfer display images in a digital format (as opposed to analog), but they do not provide the capability to supplement the display images with additional information. In particular, many known digital video interfaces do not permit the transfer of data during the blanking intervals.